First Report on the Flora of Wyouiing. 67 



under cultivation. Those of special Interest receive 

 notice in the proper place in the list, and possibly a future 

 bulletin may deal with the weed problem in this state. 



HARDINESS OF NATIVE PLANTS. 



The power to withstand frost, so remarkably devel- 

 oped in mountain floras, has undoubtedly often been 

 remarked upon before, but it is, nevertheless, unceasingly 

 a cause of wonder. To see great beds of Phlox, Merten- 

 sia, Gilia, Actinella and scores of others in full bloom at 

 times when the temperature at night is 5 '-' to 20 ° F. , 

 below the freezing point is a phenomenon that can 

 scarcely be explained. That reduced atmospheric pres- 

 sure plays an important part in preventing injury, I think 

 must be accepted, for the same plants at lower altitudes 

 would perish. The following observation goes to prove 

 this: Late in August in 1890, a plot of potatoes was 

 noted in full blossom at Mountain Home, elevation about 

 9,000 feet. Observations on three successive days 

 showed no trace of injury though on both of the interven- 

 ing nights there were heavy white frosts and films of ice 

 formed on water pails. Such a degree of cold would 

 have absolutely killed potatoes at sea-level. 



FLORAL CALENDAR. 



In 1894 every effort was made to keep pace with the 

 floral procession. At the altitude of the Laramie Plains, 

 (7,000 feet), Spring opens comparatively late. April fur- 

 nishes very few objects of interest to the botanist. The 

 earliest flowers are Phlox ceespitosa and Tozunsendia se- 

 ricea^ both of which expand their blossoms scarcely above 

 the surface of the ground. These are soon followed by 



